The invention relates to products produced by coating or casting processes that utilize cores or molds. This further includes processes in which a core and mold are utilized together to define a cavity in which product is formed. More particularly the invention relates to a lost candy method with such cores or molds in the production of such products. It also relates to an inventive candy-like composition for such core or mold material.
For example, consider products produced from coating processes that utilize cores. A core might be dipped in (or otherwise coated by) an un-set product-material, one or more times to develop one or more coats (or layers) of un-set material. After desired number of layers have been achieved (and the product material completely sets or cures), the core is removed (or eliminated) to yield the “product.” In general, the core's exterior shape gives the product its interior shape.
The foregoing assumes a core produced of a uniform material. An alternative to that is a sub-core that is coated with a skin material. The skin material provides the desired outer shape of the product. After the product is produced on this skin, then the skin material might be melted and/or dissolved away which, among other things, frees up the sub-core for extraction from the end product. The sub-core is preferably sized suitably small to navigate out of the end product without harming it because presumptively the end product is more fragile than the sub-core. To date a preferred sub-core material includes without limitation a proprietary modeling material of the Z Corporation in St. Louis, Mo., used in a stereo lithography procedure for producing complex-geometry figurines with exacting detail. Alternatively, complex-geometry sub-cores can be produced among other ways by sintering procedures when economy is more important.
In contrast, for projects with molds, an original layer of uncured product-material might be poured into and swished around the inside walls of the mold until it partially or completely sets up (or cures) sufficiently as to allow application of additional layers. After the final product shape is obtained, the mold is taken off (or otherwise eliminated) to yield the “product.” In this example, the mold's interior shape gives the product its exterior shape.
Additionally, product might be produced by casting (eg., pouring) the un-set product-material into a cavity defined between a mold and core.
There is a need for products made out of optically clear silicone or polyurethane that have precisely defined dimensions, as well as precisely defined mechanical properties. For example, there is a need for mock human-tissue tubular products that have defined change(s) in dimension against changing internal pressure. More particularly, trials with the inventive method have successfully produced models or replications of coronary artery bifurcations. Also, other trials have successfully produced models of arteries with aneurysm.
Routine trial and error with the inventive method would just as easily make replications of liver bile ducts, ventricular chambers, or any three-dimensional object that requires precisely-defined dimensions and mechanical properties.
Other fields of use or applications for end products produced in accordance with the invention include not only the utilization of such end products to test or qualify surgically-administered devices in such replicated anatomy (rather than having to test or qualify such surgically-administered devices in animal models, cadavers, or even humans) but also for demonstration purposes for companies that are selling materials or devices associated with use on, in or around these various arteries or organs. There is also great application for testing deployment of implantable devices into these inner cavities. Further possibilities include without limitation the training of physicians in use of delivery catheters or suturing.
It is known in the prior art how to produce straight tubes of constant diameter. However, the production issues with straight tubes are not nearly as complicated as with products of more complicated geometries. For one reason, it is fairly easy to remove cores out of and/or molds off of straight tubes. Yet in regards of the production of products that have complicated geometries, such as sinuous curves or large flared/hollowed-out regions in the middle of the product, the prior art is deficient in remedying the problems of successfully removing the molds or extracting the cores without compromising the integrity of the product.
That is, if the intended design is a replication of a diseased artery, as one horribly deformed by aneurysm, creating a core might not be so much a problem as separating the core from the cured replication without stretching the mock arterial walls on either side of the mock aneurysm to the point of harming the replication.
More problematical is the acceptability of a core or mold material which would allow use with specialty silicones. The preferred silicones are platinum catalyzed and are desired for producing optically clear products. Most of the catalysts used (platinum, in particular) are easily fouled by such “contaminants” as sulfur, which is contained in most living materials. Hence this excludes wax among other materials as a suitable core material. Again, wax contains matter in it which fouls the platinum-containing catalyst used to polymerize such silicones.
It is an object of the invention to overcome the shortcomings of the prior art.
These and other aspects and objects are provided according to the invention in a method of producing elastic mock human tissue products, such as arterial vessels and the like. The inventive method comprises various of the following steps. Preferably at an original time a product specification is specified, it comprising perhaps dimensions and a coefficient of elasticity. This coefficient of elasticity is some descriptive factor or measure of elastic behavior in response to a stimulus. It is additionally preferred if some test is specified which measures or determines whether such a coefficient or factor is satisfactorily met in accordance with the specification. It is further preferred if there is some original choice over the material that the produce will be produced out of. It is fairly assumed that such a material will be a suitable polymer. Accordingly, it is preferred if a polymer is specified of the type which can be obtained by a pre-polymer and polymerizing agent therefor.
Given the foregoing, the method in accordance with the invention further includes producing a batch of hard sugar-candy cores according to the specified dimensions. Small tooling is attached to the cores such as fine diameter metal hanger rods or the like. The cores are preferably dipped by the tooling into a mix of the pre-polymer and polymerizing agent in order to encapsulate the cores entirely and, for insurance, at least a small overlapping portion onto a margin of the tooling. Next the dipped cores-and-tooling are partially cured concurrently with three dimensional rotation thereof.
Further curing of the rotated dipped cores-and-tooling is preferably achieved by immersion in a bath hotter than the melting point of the hard sugar-candy cores. To see if the batch of works-in-progress meet the specification, it is preferably at this stage to select one member of the batch for testing by the specified test. This entails breaching the polymer encapsulation to melt and/or dissolve out the hard sugar-candy core. If the selected member meets the test, then the rest of the batch can be retrieved as presumptively finished product (although it is desirable to test each one for meeting the specification in order to ensure 100% quality). In contrast, it the said selected member fails but only because of insufficient polymer thickness, then the rest of the batch can be returned to the step of dipping described previously.
An example of the coefficient of elasticity has it a corresponding a percent enlargement in response to a specified pressure increase. To be particular, perhaps the product specification recites that for tubular products having an inside diameter, and the coefficient of elasticity corresponds to a 7% to 12% increase in inside diameter in response to a 100 mm of mercury pressure increase.
It is optional that the polymer might be formed by either a solvent-based pre-polymer material or a catalyst and pre-polymer combination, or both. There are available for this purpose both solvent-based urethanes or a platinum-catalyzed silicones.
The hard sugar-candy cores are produced from substantially sugar and water. It is desirable that hard sugar-candy cores have a hardness ranging from about that of glass to that of softer caramel, but nevertheless are characterized by nearly uniform solidness or alternatively the nearly complete absence of reversion into sugar crystals or sugar powder. An example composition might comprise about four (4) volume measures of sucrose to one (1) volume measure of water, and then optionally less than two percent (2%) volume measure of the whole of “anything else.” Such “anything else” might be either corn syrup or potassium tartrate, or both.
The step of partially curing the dipped cores-and-tooling concurrently with three dimensional rotation thereof preferably further comprises doing so in warm air, as well as doing so over several hours. The step of further curing the rotated dipped cores-and-tooling by immersion in a bath hotter than the melting point of the hard-candy sugar cores preferably further comprises a bath of warm water at a temperature of at least about 10° C. (18° F.) greater than the melting point of the hard sugar-candy. This additionally preferably further comprises weighting the rotated dipped cores-and-tooling for near-neutral buoyancy in such a bath.
A number of additional features and objects will be apparent in connection with the following discussion of preferred embodiments and examples.